Enhanced vibration damping by means of a negative capacitance

The use of shunted piezoelectric transducers to damp mechanical vibrations is an interesting approach thanks to its low cost and the light weight of the actuators used. Among the different ways to build the shunt impedance, the use of negative capacitances is very attractive because it allows for high damping performances with low power required by the control system. Negative capacitances do not exist as physical components but they can be designed and built using circuits based on operational amplifiers. The use of shunt circuits based on a negative capacitance coupled to a resistance allows to have a broadband control. This paper explains how to increase the bandwidth of this controller by adding to such a shunt circuit an inductance. The dynamics of the controlled system is solved analytically and the reason why the introduction of the inductance is able to give the mentioned improvement is made clear also using numerical simulations. Furthermore, this improvement also allows to increase the attenuation performance in a certain frequency band. The conditions necessary to assure the stability of the electro-mechanical system are found and explained.